1. Field of the Invention
The present invention is directed generally to mold frames for producing multi-piece solid golf balls. In general, such balls contain an inner core and outer cover with one or more intermediate layers disposed between the core and cover. The mold frames include lower and upper frame plates containing mold cavities. The interior surfaces of the mold cavities define a specific dimple pattern for the surface of the ball. A castable liquid polymer, for example, polyurethane is dispensed into the mold cavities, which are then pressed together to form a spherical cover for the ball.
2. Brief Review of the Related Art
Manufacturers produce golf balls having a wide variety of dimple patterns. Different dimple shapes, sizes, and geometric patterns are used to modify aerodynamic properties of the ball. The dimples affect the lift, drag, and flight stability of the ball. When a golf ball is struck efficiently with the club face, it will spin about a horizontal axis and the interaction between the dimples and oncoming air stream will produce the desired lift, drag, and stability. Various dimple patterns are used to create a ball that can travel long distances and have good flight trajectory when struck by a club.
Forming the dimpled cover layers for golf balls involves several steps. Mold cavities having select dimple profiles are used to manufacture the balls. The mold cavities have slight protrusions machined into their interior surfaces and these peaks/valleys form the dimple pattern on the surface of the ball. In large scale production operations, thousands of balls are produced daily. It is important the dimples be formed consistently on the ball surfaces. The dimensions and geometries of the dimples must be identical for each ball being produced on a given assembly line. In turn, the dimple profiles of the mold cavities used to produce these balls must be precisely detailed and accurate.
In the past, compression molding frames containing bores and channels which penetrated through rows of mold cavities were used to form the ball covers. The golf ball cores were placed in mold cavities that were loaded into the frames. Half-shells of the cover material such as balata or ethylene-based ionomer resins were placed in the cavities. Then, a thermal medium such as steam was fed into the bores and channels to melt the cover material. The resulting balls were cooled with cold water and then unloaded from the mold. Brown, U.S. Pat. No. 4,558,499; Reid, Jr., U.S. Pat. No. 5,725,891; and Reid, Jr., U.S. Pat. No. 5,795,529 disclose such thermal/cooling mold frames.
In recent years, mold cavities containing a castable liquid polymer that are placed in a mold frame have been used for molding the cover material. In these methods, a castable polymer material such as polyurethane or polyurea is mixed and dispensed into the mold cavities For example, Hebert et al., U.S. Pat. No. 6,132,324 discloses a method of forming a multi-layered golf ball comprising a core, inner cover layer, and outer cover layer. The core of the golf ball is formed and then an inner cover is injection-molded over the core to form a golf ball subassembly (core and inner cover). Two mold cavities are used, an upper mold cavity and lower mold cavity. Each mold cavity is approximately one-half of the size of a finished ball. The mold cavities have interior walls with details defining the dimple pattern of the resulting ball. A castable polyurethane material is introduced into the mold cavities and then the ball subassembly is placed in one cavity.
Next, the upper and lower mold cavities are joined together under sufficient heat and pressure to form an internal spherical-shaped cavity. The polyurethane material in the cavities encapsulates the ball subassembly and forms the cover of the ball. As noted above, the mold cavities, which are pressed together, contain slight protrusions representing the negative image of the dimple pattern that will be produced on the finished ball. The mold cavities are held together until the polyurethane cover material is cooled, and then the cavities are opened to remove the ball.
Referring to FIG. 1, a golf ball mold (10) of the prior art used to form a traditional cover layer over a core (or ball subassembly) is generally shown. The mold (10) includes hemispherical mold cavities (12) and (14) having interior dimple patterns (12a) and (14a). When the mold cavities (12, 14) are mated, they define an interior spherical cavity (16) to form the cover for the ball. The mold cavities (12, 14) are mated together along a parting line (17) that creates an equator or seam for the finished ball. In recent years, mold cavities with non-planar mating surfaces have been used to create a golf balls having a staggered parting line. For example, Nardacci et al., U.S. Pat. No. 7,618,333 discloses a method for making golf balls having a staggered parting line. The upper and lower mold cavities have non-planar mating surfaces. When the cavities are mated, the parting line follows the dimple outline pattern and allows the dimple outline pattern of one mold cavity to interdigitate with the dimple outline pattern of the mating mold cavity, thereby forming a golf ball without an obvious parting line.
In FIG. 1A, the mold cavity (14) is shown in further detail. The mold cavity (14) includes a dimple pattern (14a) and locator slot (18) that fits over a locator pin on a mold frame (not shown) when the mold cavity (14) is inserted into the frame. In conventional molding operations, the upper and lower mold cavities normally have the same design. That is, a given mold cavity may be used in either the upper or lower mold frame. These “single-design” cavities may be used interchangeably in the upper and lower mold frames. Fabricating single-design cavities minimizes manufacturing time and cost; improves part consistency; and makes assembly of the mold frame easier. Each mold cavity has a hemispherical structure and contains one-half of the dimple patterns. When the two mold cavities are pressed together, they produce a complete dimple pattern on the ball's cover.
Referring to FIGS. 2 and 3, the mold cavities (12, 14) are placed in traditional lower and upper mold frame plates (20, 30). In FIG. 2, a conventional lower mold fame plate (20) is shown. The frame plate (20) includes four circular recessed portions (22a, 22b, 22c, and 22d) for receiving four mold cavities (14). Each recess includes a locator pin (24a, 24b, 24c, and 24d) for inserting into locator slots arranged in the mold cavities. The frame plate (20) further includes threaded bores (25a, 25b, 25c, and 25d) for receiving bolts (not shown) so that the lower and upper plates (20, 30) can be clamped together. In addition, the frame plate includes two cut-out cavity hold areas (26, 27) for placing a retainer washer. This retainer helps to secure the mold cavities in place and keep them level after being placed in the mold frame. Alignment holes (28, 29) are located in corners of the lower frame plate (20). Guide pins in the upper frame plate (30) are inserted into the alignment holes (28, 29) to facilitate attachment of the upper plate (30) to the lower plate (20).
In order to maintain the dimple pattern design and provide a staggered parting line, there needs to be a certain rotation angle (α) between the mold cavities (12, 14). Conventional mold frames provide the proper rotation angle (α) between lower and upper mold cavities by way of locator pins. These pins are located in select areas of the lower and upper mold frames. The locator pins are inserted into locator slots of the mold cavities to secure the cavities in place. The locator pins/slots ensure the mold cavities are correctly aligned. In particular, the mold cavity (14) shown in FIGS. 1 and 1A can be rotated 42°, 114°, 186°, 258° or 330° (counter-clockwise direction) so that it is properly aligned with the opposing mold cavity. In the mold frame, however, it is desirable to maintain the locator pins towards the center of the mold frame to ensure positive cavity alignment; thus, rotation angle (α) values of 330° and 42° are used.
In FIG. 3, a conventional upper mold frame plate (30) is shown. As discussed above, the frame plate (30) includes four circular recessed portions (32a, 32b, 32c, and 32d) for receiving four mold cavities (12). Each recess includes a locator pin ((34a, 34b, 34c, and 34d) for inserting into the locator slots of the mold cavities. The frame plate (30) further includes threaded bores (35a, 35b, 35c, and 35d) for receiving bolts (not shown) so the lower and upper plates (20, 30) can be clamped together. In addition, there are two cut-out cavity hold areas (36, 37) for placing a retainer washer. Guide pins (38, 39) are inserted into the slots (28, 29) of the lower frame plate to register the upper and lower frame plates.
As discussed above, the mold cavities (12, 14) have the same design. Thus, the mold cavity (12) can be placed in either the lower or upper frame plate. Likewise, the mold cavity (14) can be placed in either the lower or upper frame plate. This single cavity design is desirable because it means the mold cavities (12, 14) can be used interchangeably in the upper and lower mold frame plates (20, 30). On the other hand, this configuration may lead to problems with accurately positioning the mold cavities in the mold frames to produce certain dimple layouts. Particularly, because any slot in a mold cavity can be fitted with any locator pin in any frame plate, this may lead to the cavities being placed in the wrong position. As a result, the desired dimple pattern may not be created on the surface of the ball.
In the lower frame plate (20) (FIG. 2), a single pin (24a-d) is located on each circular recess of the plate. The pins are located at 330° and 42° from a vertical axis. Meanwhile, the upper frame plate (30) (FIG. 3) has a single pin (34a-d) located on each circular recess, each pin being arranged on the vertical axis. Thus, the mold cavity (12, 14) must be positioned on either frame (20, 30) so the slots of the mold cavity are aligned with and fit over the pins. This mold frame design is generally well suited for molding golf balls having a modified-icosahedron dimple layout. That is, this configuration of the lower and upper frame plates (20, 30) is generally effective when each mold cavity (12, 14) has a modified-icosahedron dimple pattern. However, this mold frame configuration is generally ineffective for other dimple patterns.
For example, FIG. 4 shows a conventional mold cavity (40) for producing a dimple layout based on a tetrahedral geometric pattern (42). This mold cavity (40) includes three identically-sized locator slots (45a, 45b, and 45c). For this dimple pattern, the cavities must be assembled in the frames such that:                Slot (45a) mates with the pins located at the rotation angle (α) of 330° on the lower frame plate (20);        Slot (45b) mates with the pin located in the upper frame plate (30); and        Slot (45c) mates with the pins located at the rotation angle (α) of 42° on the lower frame plate (20).        
That is, any slot in the mold cavity can be aligned with any locator pin in any frame plate. Since any slot can fit over any locator pin, it is possible the correct slot may not be fitted with the correct pin. This is particularly a problem when an operator in the production line is not familiar with the dimple pattern layout and inserts the mold cavity in the wrong position. If a mold cavity is placed in the frame so that a given slot is fitted improperly over a locator pin, this will cause the lower and upper mold cavities to misalign. Improperly aligned lower and upper mold cavities can damage the mold cavities resulting in golf ball defects. Thus, there is a need for a mold frame having a more robust and accommodating structure. The mold frame needs to be able to accommodate mold cavities having various dimple layouts and prevent or minimize the likelihood of misaligned mold cavities. In addition, the mold frame needs to be accommodating to single-design mold cavities. That is, a given mold cavity needs to able to fit in the upper and lower mold frames. The present invention provides a mold frame having these features along with a method of molding golf balls using this frame. These and other objects, benefits, and advantages of the invention are evident from the following description and illustrated embodiments.